Provided is a diffusion system for forming a doping layer in a wafer. The diffusion system includes a bubbler for generating a doping gas; a premixer, which premixes the doping gas with reactive gases and preheats the gas mixture; a main chamber, in which the gas mixture reacts to the wafer; a buffer case, which externally isolates an exhaust port and a door for loading and unloading the wafer into and out or the main chamber; and a used gas exhaustion system, which exhausts a used gas after the reaction is finished in the main chamber.